Heating, ventilation and air conditioning (“HVAC”) systems are commonly used in many climate control applications. Air Handling Units (AHUs) are one of several components in HVAC systems. They are an important component as the AHU houses a number of components used in the system to provide forced air for climate control in a particular structure. AHU components typically include motors, heating/cooling coils, and blowers as well as the required interface connections to these components to effect such climate control.
The AHU is an enclosed interconnected framed panel structure. The framed panel structures have insulated panels that are supported between framing members, also referred to as raceways, to define interconnected rectangular compartments. Typically, the insulating material used in the panel is polyurethane foam that may be installed as a block, or injected as a foam, which cures to form a core within the panel.
Polyurethane foam insulation has superior insulating and indoor air quality (“IAQ”) properties versus fiberglass insulation. Although fiberglass has been the insulation of choice in many industries, foam insulation has become favored over fiberglass due to its reduced construction costs and increased energy savings potential. Foam insulation is currently heavily utilized in many industries, including household appliances (refrigerators, freezers), walk-in coolers (grocery stores, food processing plants) and HVAC units (AHUs and packaged products). However, a significant drawback to foam-insulated products is smoke generation when subjected to elevated temperatures, such as those generated during a fire. Smoke generation, or smoke spread, by foam-insulated panels is significantly increased with panels having thicknesses exceeding approximately one-half inch to one inch, depending upon the type of insulating material used, which thickness is typically exceeded to provide adequate insulating performance. While additives may be added to the foam insulation mixture to enhance flame retardant characteristics, those same chemicals typically adversely affect the smoke spread characteristics.
Flame and smoke generation indexes are predominantly measured utilizing a test conducted in accordance with the procedure outlined by the American Society for Testing and Materials in ASTM E 84-01, “Standard Test Method for Surface Burning Characteristics of Building Materials” (the National Fire Protection Agency in NFPA 255, the American National Standards Institute/Underwriters Laboratories in ANSI/UL 723 and the Uniform Building Code in UBC 8-1).
The index is based on a standard that is given a value of 100, such as red oak having a pre-determined moisture content. Therefore, any measured index value is compared to the standard value, and typically, fractional portions of the standard value are selected as classifications within an industry. Different industries permit differing levels of flame and smoke generation. The walk-in cooler industry, for instance, uses standards that allow a smoke generation index as high as 450 per ASTM E84, which can be easy to achieve, but uses a flame spread designation that is typically classified as Class I, which corresponds to a flame spread index of no higher than 25, or one-fourth of the index of red oak. Thus, walk-in cooler industry places more emphasis on the rate of flame spread as a measure of safety.
A low flame spread index can be achieved in foam-filled panels by mixing the foam with readily available flame-retardants. Foam insulation for panels and walls with one-half inch thickness or less typically contains a minimal amount of foam insulation material, thus enabling the panel to pass the common 25 flame and 50 smoke index requirements of NFPA 90A per ASTM E84. However, foam-insulated panels and walls greater than one-half inch in thickness must typically use additional materials or components to minimize heat transfer, and lower smoke generation index values to meet the above smoke index requirement, or utilize agency listings (UL, Environmental Technology Laboratory (“ETL”)) to provide “proof” of safety. To provide the required amount of insulation, panels used with HVAC systems must typically be substantially thicker than one-half inch.
Per standard building codes, the outer casing material of panels for HVAC systems must typically provide a 15-minute flame barrier, such that the flame does not come into direct contact with the insulating material, if present, which is typically flammable material. However, even with outer casing materials that provide a 15-minute barrier, the flame/smoke performance characteristics of the panel typically do not sufficiently improve. That is, without an additional thermal barrier material or component, a foam panel insulation system will not meet the 25/50 flame/smoke generation requirements of NFPA 90A per ASTM E84.
What is needed is a thermal barrier material or component that can be used with household appliances, walk-in coolers and HVAC units and provides improved flame/smoke performance characteristics.